Ion beam milling systems are used for the preparation of specimens whose internal and surface structures are then analyzed using a transmission electron microscope (TEM) or scanning electron microscope (SEM). Many techniques have been developed which have included the use of mechanical cutting, grinding, and/or polishing operations in combination with ion beam bombardment. In many instances, such techniques have required that the specimen be repeatedly moved from one apparatus to another (either different preparation devices or observation devices) and/or be moved or realigned while mounted in a cutting, grinding, or milling device.
Ion beam milling systems have been used to prepare specimens of various materials including ceramics, semiconductors, metals, and combinations thereof. One method of ion beam milling is slope cutting, wherein an ion beam is directed at a masking screen located at or near a specimen surface. The masking screen, which is typically mounted at an angle to the specimen surface presenting a “knife edge,” protects a portion of the specimen, while the remainder of the specimen is milled by the ion beam, which passes the knife edge to reveal desired profiles. This technique is capable of providing cross-sectional profiles of layered structures, the surfaces of which can then be studied by scanning electron microscopy. For example, Hauffe, East German published Patent Application No. 201,538, teaches an apparatus and method for preparing specimens for SEM analysis by providing an ion gun inside the specimen chamber of a scanning electron microscope. A mask is positioned adjacent to the sample and is used, in conjunction with the ion gun, to remove material from the specimen.
Mitro et al, U.S. Pat. No. 5,922,179, teaches an apparatus and process for etching and coating specimens in a single vacuum chamber, to minimize handling and transfer. The apparatus includes a sealed chamber and a vacuum pump for forming and maintaining a vacuum in the chamber, a first ion gun positioned in the chamber to etch a specimen, a sputtering target in the chamber, and at least one additional ion gun positioned in the chamber to cause material from the target to be directed onto the specimen.
Techniques have also been developed in the preparation of specimens for scanning electron microscopy in which the specimen may be observed by a SEM during preparation thereof. For example, Grunewald, U.S. Pat. No. 5,986,264, (“Grunewald”) teaches an ion beam milling system using two ion guns for use in the preparation of samples to be used in both SEM and TEM analysis. The system uses an SEM as a high resolution imaging device to observe the progress of the ion milling of a sample and to determine when a proper sample thickness has been achieved. Also, as the sample stage can be tilted, the system is also useful for slope cutting of specimens. Grunewald, however, does not disclose a device that allows SEM imaging of the in situ adjustment of a slope cutting screen and then ion beam milling in a dedicated ion beam milling device and subsequent high resolution imaging of the milled specimen in the SEM. Rather, Grunewald discloses “an ion beam preparation device for electron microscopy which is capable of observing the milling process in-situ with the aid of a scanning electron microscope.”
All references cited herein are incorporated by reference as if fully set forth here.
Typically, ion beam milling systems require that the ion milled specimens be removed from the specimen holders for use in the milling device and loaded in a TEM or SEM holder for imaging. Clearly, loading and unloading of the specimen from the holders increases the potential of damage to fragile specimens. Multiple milling steps may be required, depending upon thickness requirements at the area of interest in the specimen, thus increasing the risks and contamination associated with transfer of the specimen. Thus, a need exists for a system wherein ion beam milling can be performed in the same vacuum environment as the focused beam microscope and where the relative position of the specimen and slope cutting screen can be adjusted in situ within the microscope for such subsequent milling.